Method of protecting metal surfaces against abrasive wear



United States Patent 3,414,517 METHOD OF PROTECTING METAL SURFACES AGAINST ABRASIVE WEAR Benjamin Mosier, Houston, Tex., and Miles R. McCorkle, Qswego, Paul L. Du Brow, Chicago, and Byron E. Marsh, Western Springs, Ill., assignors, by mesne assignments, to Armour Industrial Chemical Company, a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 341,435, Jan. 30, 1964. This applicafion Dec. 15, 1966, Ser. No. 601,833

4 Claims. (Cl. 252-33) ABSTRACT OF THE DISCLOSURE Dilute solutions of water-soluble sulfonated fatty acid esters (viz. the methyl ester of alpha-sulfo stearic acid and its sodium salt) are employed in aqueous mediums to protect metal surfaces, particularly the wear surfaces of submersible oil well pumps, against abrasive wear. The sulfonated fatty acid esters contain the sulfur in a CS linkage, as distinguished from the C--OS linkage of sulfated fats.

Cross-reference This application is a continuation-in-part of copending application Ser. No. 341,435, filed Jan. 30, 1964, now abandoned.

Background of the invention In recent years hydraulic pumping systems for oil wells have gone into widespread commercial use. These systems utilize subsurface pumps which are positioned within the oil well casing near the production stratum. The moving parts of these pumps operate with very close tolerances, and the problem of abrasive wear is severe, especially when a brine or saline solution is employed. Brines are not ordinarily usable as hydraulic fluids because of their corrosive nature.

Chemical agents for use in lubricating submersible oil well pumps should be water-soluble or dispersible so that they can be introduced into the aqueous hydraulic fluid at the surface of the well, and the chemical agent must be adsorbed on the metal surfaces to be lubricated at the hydraulic fluid circulates over these surfaces. The chemical agent, after adsorption on the metal surfaces must function as a highly effective lubricant, that is, it must reduce abrasive wear between the surfaces. The lubricant should also have the property of remaining on the metal surfaces under a high applied pressure or torque, as would be generated between the relative moving metal surfaces of the pumps. In other words, the lubricant should have good boundary properties to minimize wear and to prevent any increase in the tolerances of the contacting parts, and it should also be effective as an extreme pressure lubricant so that it is not squeezed off of the surfaces or desorbed at torques of greater than 60 to 80 inch-pounds.

Summary of the invention This invention provides a method of lubricating metal surfaces wherein the lubricating agent possesses all of I 3,414,517 Patented Dec. 3, 1968 abrasive wear by depositing a coating on the metal surface of an ester of a sulfonated fatty acid. The sulfonated fatty acid esters contain the sulfur as a CS linkage as distinguished from .a CO-S linkage which characterizes organic sulfates. The coating is in the form of a thin film, which may be substantially a monomolecular layer, and this film or layer is formed by contacting the metal surface with an aqueous solution or dispersion of the sulfonated fatty acid ester. Apparently the lubricating agent forms a coordination compound with the negatively charged metal surface. The method is not limited to ferrous metal surfaces, but can be applied to all structural metals and metal alloys.

Description of preferred embodiments The sulfonatecl fatty acid esters useful in practicing the present invention are those which can be prepared from naturally occurring fatty acids and fatty acid mixtures. The fatty acid group will therefore contain from 8 to 22 carbon atoms. For the purpose of the present invention, fatty acids or fatty acid mixtures composed predominantly of fatty acids having from 12 to 18 carbon atoms are especially desirable, particularly the fatty acids containing 16 or 18 carbon atoms. For example, the fatty acid groups may be palmityl, stearyl, or oleyl. While both saturated and unsaturated fatty acid groups can be employed, the saturated fatty acids are preferred. It may therefore be desirable in certain preferred embodiments of the present invention to hydrogenate the naturally occurring fat or fatty acid mixture obtained therefrom until a high degree of saturation is obtained. For example, tallow can be hydrogenated to convert the oleic acid therein to stearic acid, thereby resulting in a fatty acid mixture composed primarily of stearic acid, together with a lesser proportion of palmitic acid.

The lubricating agents of this invention will contain at least one sulfonate group, such as can be introduced into a fatty acid by treatment under appropriate conditions with sulphur trioxide, as is well known in the sulfonation art. Sulfonated fatty acids are available commercially. For saturated fatty acids, the sulfonate group is bonded to the alpha carbon, while for unsaturated fatty acids, the sulfonate group is attached to one of the double bonded carbon atoms. The sulfonated fatty acid esters contain the sulfur as a CS linkage. Thus the compounds are quite distinct from sulfated fats which contain the sulfur in a C-OS linkage. Sulfated fats are formed by reaction with sulfuric acid rather than sulfur trioxide.

As used in this invention, the sulfonated fatty acids are in the form of water-soluble or water-dispersible esters. Esters of short chain alcohols or glycols are preferred, but esters of polyethylene glycol can be employed where the ester group has a longer chain length. For example, the ester group may be an aliphatic hydrocarbon containing 1 to 6 carbon atoms, or the ester may be a hydroxysubstituted aliphatic hydrocarbon containing from 2 to 6 carbon atoms. By way of specific example, the ester group may be methyl, ethyl, propyl, monoethylene glycol, or propylene glycol. The alkyl or hydroxyalkyl ester group advantageously can contain less than 3 carbons; viz., the methyl, ethyl and hydroxyethyl esters. Where the ester group is a polyethylene glycol chain or residue, the polyethylene glycol group should have a molecular weight of less than 2,000, and optimally not over 1,000. The ester group should not be so hydrophobic as to make the lubricating agent water-insoluble or non-dispersible.

The sulfonate group may be in its free acid form or in a salt form. The sodium, calcium or ammonium salts are particularly desirable because of their relatively low cost, but other salts can be used, such as the salts of the alkali metals, the alkaline earth metals, etc. The salt form can be advantageous in providing increased water solubility.

Particularly desirable compounds for use in the method of this invention are the alpha-sulfo esters of saturated fatty acids containing from 12 to 18 carbon atoms, particularly the palmitic C and the stearic acid C derivatives. The methyl or ethyl ester and the mono ethylene glycol hydroxyethyl ester of such compounds meet superlatively well the exacting specifications of lubricants for subsurface hydraulic oil well pumps. The sodium salts of alpha-sulfo stearic or palmitic acids are outstandingly effective, especially when employed as their methyl or hydroxyethyl esters.

In practicing the method of this invention, the lubricating compound is dissolved or dispersed in water or in a saline brine, or more generally in the aqueous phase of a fluid medium, which may consist of an oil and brine mixture, or a pumpable drilling mud having an aqueous phase, etc. The concentration of the lubricating agent in the water or the aqueous phase of the fluid medium should be sufficient to provide for the coating of the metal surfaces to be protected against abrasive wear. Usually, the water or aqueous phase should contain at least 50 p.p.m. (parts per million) of the lubricating compound, and in most applications, it will usually be preferable to employ at least 80 ppm. of the lubricating compound. Usually, it will not be necessary or desirable to use concentrations greater than 500 to 1000 p.p.m. For use in oil well subsurface pumps where the lubricating compound is introduced into the brine employed as the hydraulic fluid, concentrations of from 50 to 500 ppm. are satisfactory. For example, good results have been obtained in such applications with concentrations ranging from 100 to 200 ppm. of the sulfonated fatty acid ester. The aqueous phase containing the lubricating compound is contacted with, or preferably circulated over, the metal surface to be protected against abrasion. If desired, the surface may be continually treated with the water or aqueous phase containing the lubricating compound, thereby tending to maintain the desired protective layer or film of the lubricating compound during operation of the pump or similar apparatus.

wherein x is a numeral from 5 to 19 and preferably from 13 to 15, R is an ester group such as a straight or branched chain aliphatic hydrocarbon having from 1 to 6 carbon atoms, or the residue derived from a glycol having from 2 to 6 atoms, or the residue derived from a polyethylene glycol moiety of not over 2,000 molecular weight and preferably not over 1,000 molecular weight, and M is hydrogen or a salt forming radical such as an alkali metal, an alkaline earth metal and ammonium.

Where the lubricating agent of this invention is derived from unsaturated fatty acids, such as oleic acid, the compounds may be represented by the following structural formulas:

wherein x and y are integers from 1 to 17 and preferably from 1 to 13, the total or x+y equalling 4 to 18 and preferably 12 to 14. The other variables R and M have the same meanings previously assigned with respect to Formula 1. Since the carbon atoms on either side of the double bond are susceptible to sulfonation, the sulfonation of an unsaturated fatty acid, such as oleic acid, will usually result in a mixture of compounds having the Formulas 2 and 3. While the unsaturated linkage for oleic acid is usually regarded as being between the 9 and 10 carbon atoms, the double bond is not entirely fixed in this location, and may migrate to other positions over the range indicated. The mixed sulfonated product will contain at least small proportions of compounds where the sulfonate radical is attached to carbons other than the 9 or 10 carbons.

The lubricating and wear-resistant properties imparted to metal surfaces by the method of this invention are illustrated 'by the data set out below in Table A.

TABLE A.WEAR REDUCTION PROPERTIES Weight loss (mg. in 5 min.) at applied torque (in-lb.)

Lubricating agent in oil well rine Brine alone 0. 4 4. 0 Galls at SAW 30 motor oil 1 0.1 0. 2 0.3 Galls.

Monoethylene glycol ester alpha- 1 0.1 0. 2 D0.

sulfo stearic acid (0.02%).

Monoethylene glycol ester alphn- 1 0.1 0. 2 0.6 Galls at 180.

sullo stearic acid (0.01%).

Polyethylene glycol ester (200 0.1 0. 3 0.4 at 180. Galls at 240.

M.W.) alpha sulfo stearic acid I i' i% i 1 1 t 1 000 1 0 ye y eneg yco es er 0.1 0.1 0.7 at 18 G lls. M.W.) alpha-sull'o stearic acid 0 a (0.02%).

Monoethylene glycol ester of 0. 1 0. 2 0.6 at 140.... Galls at 240.

alpha-sulfo stearic acid (0.02%).

Methyl ester alpha-sulto stearic 1 0.1 0. 2 0.3 at 140.-.. Galls at 250.

acid (0.02%).

Same in fresh water (0.01%) 0. 2 0. 4 0.1 at 180.-.. Galls at 310.

Mixed Polyethylene glycol esters 1 0.1 0. 2 0.4 at 140. Galls at 220.

of alpha-sulfo stearic acid Calcium salt of methyl ester 1 0. 1 .1 Gall alpha sulfo stearic acid (0.02%). s at 360 N-butyl ester alpha-sulio stearic 0.1 0. 4 0.2 at Galls at 200.

acid (0.02%).

N pr0pyl ester alpha-sulio stearic 0.1 0.3 0.5 at Galls at 240.

acid (0.02%).

Sod. salt methyl ester alpha-sulfo 0.1 0.1 0.3.. 0.1.

stearic acid (0.2%).

Sod. salt methyl ester alpha-sulio 0.1 0.1 0.4 0.2 (galls at 240).

stearic acid (0.01%).

1 Less. Lubricating agents derived from saturated fatty acids usable in the present invention can be represented by the 70 following structural formula:

The foregoing tests were conducted on a Baroid Mud Tester, which is similar to a Timken Wear Tester. A standard test procedure was followed wherein the test (1) 0 block Was mounted on a torque arm of the apparatus, CH3(CHI)XCH (LL OR and brought 1nto contact with the ring mounted on a 50 M 75 shaft, which 1s rotated at a constant speed. In each t t one side of the block was forced against the test ring at a specified torque for a specified time. During the test, both the block and ring are immersed in the solution containing the lubricating agent at the specified concentration. The test block is Weighed before and after the test to determine the weight loss. When galling or seizing occurred between the contacting parts, the test was discontinued without further increase in torque. The torque represents the force applied to the test block by the ring, and is measured on the torque arm.

Additional data was obtained using the Baroid Mud Tester by procedures similar to that just described. This data is summarized in Table B.

TABLE B.BAROID MUD TESTER WEAR DATA The method of this invention is further illustrated by its application to the lubrication of subsurface hydraulic pumps in oil well production operations. The methyl ester of alpha-sulfo stearic acid, either as the free acid or as its sodium salt, is employed as a lubricant in the aqueous power fluid at a concentration of from 150 to 200 p.p.m. The power fluid may be salt water or fresh water. Before circulation to the subsurface pump, the power fluid will be kept in one or more surface tanks, and is therefore convenient to introduce thelubricating agent into the fluid while it is under surface storage. For a socalled open system the fluid will only be circulated once, and therefore it is a simple matter to achieve the desired concentration introducing the lubricating agent into the fluid before it is circulated. For a closed system Where the aqueous hydraulic fluid is recirculated after it has been separated from the oil, there may be some residual lubricating agent in the fluid, and it may be desirable to add only suflicient lubricating agent to make up the concentration to the desired level before the fluid is recirculated. Alternatively, a higher than necessary concentration can be employed for the initial circulation, such as a concentration of 500 to 600 p.p.m., and the fluid can be recirculated until the concentration drops below the desired level for maximum lubricating protection. With this procedure, make-up lubricating agent need only be added periodically. If desired, an auxiliary corrosion inhibitor can also be incorporated in the circulating fluid. The procedure just described is applicable to various commercial subsurface pumps, such as those supplied by the Fluid Packed Pump 00., a division of the National Supply Company, or by Kobe, Inc.

While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof and many details have been set forth for the purpose of illustration, it will be apparent to those skilled in the art that the invention is susceptible to other applications and embodiments and that many of the details described herein can be varied considerably without departing from the basic principles of the invention.

We claim:

1. In a method of lubricating metal surfaces subject to abrasion wherein a fluid medium providing an aqueous phase is contacted with said surfaces, the steps comprising introducing into the aqueous phase of said medium from to 500 p.p.m. of a water-soluble ester of an alphasulfo fatty acid wherein the fatty acid groups are saturated and contain from 16 to 18 carbons, the ester groups thereof being selected from the class consisting of aliphatic hydrocarbon groups containing from 1 to 6 carbons, hydroxy-substituted aliphatic hydrocarbon groups containing from 2 to 6 carbon atoms, and polyethylene glycol groups having a molecular weight of less than 2,000, and contacting said aqueous phase with said metal surfaces.

2. The method of claim 1 wherein said metal surfaces are the wear surfaces of a submersible oil well pump, and said fluid medium is circulated over said surfaces.

3. The method of claim 2 wherein said ester is the methyl ester of alpha-sulfo stearic acid, the sulfonate group thereof being in its sodium salt form.

4. In a method of lubricating metal surfaces subject to abrasion wherein a fluid medium providing an aqueous phase is contacted with said surfaces, the steps comprising introducing into the aqueous phase of said medium a Water-soluble ester of an alpha-sulfo fatty acid wherein the fatty acid groups are saturated and contain from 16 to 18 carbons, said ester being present in said aqueous phase in a dilute concentration effective for coating said metal surfaces and the ester groups thereof being selected from the class consisting of aliphatic hydrocarbon groups containing from 1 to 6 carbons, hydroxy-substituted aliphatic hydrocarbon groups containing from 2 to 6 carbon atoms, and polyethylene glycol groups having a molecular weight of less than 2,000, and contacting said aqueous phase with said metal surfaces.

References Cited UNITED STATES PATENTS 2,914,975 12/1959 Cavanaugh et a1. 25233 XR PATRICK P. GARVIN, Primary Examiner. 

